Radiotelephony



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Patented May 10, 1927.

raiser o ar es.

PAUL \VARE, OF YORK, 'N. Y., ASSIGNO-R 'IO WARE RADIO, INQ, OF NEW YORK,,.N. lY.,-A GORPOEATION OF DELAWARE.

.RADIOTELEPHONY.

Application filed September 3, 1921. Serial No. 4%,339.

Thisfinvention relates to duplex or twoway radio com-mun-ication, moreparticularly to 'communication by telephone, wvherem communication canbe had over considerable space, =wah0utmanipulation of switches orvarying circuit conditions as between sending and receiving, in.azmanner similar to present day wire telephone communication.

The 3 invention employs at a station a power radiating element orantenna separate from' the element receiving incom ng oscillations,herein shown as a loop which i has *especial advantages in the systemherein disclosed over an ordinary: antenna for receivingy-aswill behereafter pointed out. T-he'objeets of the invention generally are toenable separate transmitting and I'GCelV- in}: elements to be'installedwithin reasonable distance of eachother, as in the samebuilding,without causing the receiving system to be paralyzed by thepowerful transmitting system, while maintaining the necessary'sensitiveness to provide an efficient system wherein'power losses arereduced to a minimumyiand also to provide a system Which 'w-ill requireno radio skill to operate and which" can be easily set up and used inoutlying districts or where space is limited Without requiring a largefixed plant or ground area. Sue-ha system is herein provided wherein thetransmitting element can be on the roof of a build-ing andi thereceiving loop element either on thesame root, or within one of therooms without' interfering one with the other and each stationbperated'by'automatically or manually controlled batteries andja dynamotor, thebatteries being' chargeable whenthe system is notiin operation fromany'suitable source: of power.

j-Sofar as'I am aware; there is nosystem as above outlined at present onthe market er -available in the'art, notwitl-istanding that there is anenormous field't'or such'a-system either-"for telephoniccommunication indistricts without any electrical communication at all -or"where presentwiretelephones and telegraphs are more expensive or toowrestricted inoperation,- or whereit is desired to extend thepresen't radius ofcoiunninication of wire telephones by radio. The circuits of thissystemiare so arranged that they can be attached to ordinary wiretelephone circuitspwhiclrhas heretofore been a r difiiculty in duplexradio extensions ofai'ire telephones.

In carrying out the invention, both the transmitting and receivingcircuits are improved in various particulars, together with novelmeansconfining the various currents to their own proper circuits, andfor-shielding and protecting the receiving equipment from undesirablecoupling with adjacent metallic objects such as pipes, frames ofbuildings, fixtures, etc, which might carry transmitter high frequencyenergy.

Any suitable source of; power maybeused for.transmitting, but as shownherewith, a storage battery and dynz-imotor, having suitablemeans forQlllllll'lltlllgdtS ripple, are

provided. The transu'iitte'r includes master oscillator, poweramplifier. and power zr'nodulator vacuum tubes, the circuit containingsuch tubes beingpreferably loosely coupled through an adjustable outputtransformer to the-transmitting element radiating continuous carrierwave oscillations. The telephone transmitter is adjacent the telephonereceiver, as in wire telephony, and is connected in circuit with theprimary of a modulation transformerwhosc secondary: is connected"withthe power modulator and remainder or the t'ansmitting'cireuit. .Animportantieature of this transmitting-systenr' is that ibis-tree ofoperating adjustments, beingset once for all and operating withoutskilled attention under iinten'ded conditions.

Although an ordinary receiviim antenna may be used with such atransmitti-np system, a loop 'receii-"ing element has a number ofadvantages, especiallyior duplex operation. The improved loop"receiving;arrangementin conjunction with the transmitting highfrequency circu'it localized auljacent, the antenna asdisclosed herein.has the additional advantage, 'ho'wever, of permitting much more closelysituated sending: and receiving, equi 'nnentunder conditions encouutered in practice than has heretofore been possible'to obtain. Apreterre'd arrange-- ment is to 'localive the trznismitting highfrequency equipment in a weather proof box at the antenna, as on theroot of a building. The transmitting vacuum tubes should be in aseparate ventilated but burglar proot compartment of this box. The loopreceiver and its associated radio frequency circuits may also be out ofdoors, but it is of advantage to locate it indoors, especially if astorirejc battery is used to heat the receiving tube filaments and it isdesired to locate this storage battery at the Jor-iition oi thetransmitting storage lnatteiy. as herein provided, because it the rcce'p; circuit is locatx near the battery position there will be less powerloss in the coiuiectiue; lines and. consequently a snuillcr battery isretpiired than otherwise.

By a novel. system of shielding: and the utiliaation of a loop of smallsize I am able to install the receiving set in an ordinary room withoutatl'ecting its sensitivcness or permitting it to he atlected byinduction iron] the local transmitter. as through the frame (it thebuilding, pipes, and other metallic objects. The receiving system.contains a. loop with its flat side approximately toward the antenna topick up a. minimum of transmitter energy, and pointing: to the distantstation and is preferably of the beterodyne type, as shown, whereinlocal oscillations derived from the transmitter. or preferably from aseparate local oscillator. are of such difference in frequency from thevoice modulated. incoming: oscillations as to produce a. voice modulatedsip'i'ial beatiirequcncy. which is preferably out of andibihtyfrequency, this heat tl'requency being; amplitied by one or moreamplifiers, and. finally demodulated or translated into the desirablevoice frequencies in the telephone receiver.

l have "Found that a. small eloctrostatically shielded loop of-noveltorm can be installed. in a room with the receiving tubes,transfin-rmn-s, etc, inside the, loop for compactness it desired,without being affected. by adjacent pipes, columns, gras meters, etc.,with successful results, thus providing; a high frequency duplextelephonic communication system througl'i space, using' a desk telephoneset automatically controlling the power unit from the desk set hook andcompletely eliminating all operating: adjustments, throw-over switchesor the like.

The matter of eliicicncy is important in automatically controlledsystems of this character, which must operate for considerable timewithout attention, because thus far only the smaller sizes of vacuumtubes have been developed to operate on reasonably low plate voltagesthat are satisfactory for this SGI'V'ICC.

In this system, the transmitting high frequency is isolated to thetransmitting radiating system, eliminating the customary leadin wires,as on the roof, it the installation is made on and within a building,While a novel system of sheathed cables connecting the several unitseilectively prevents inter- :t'erences.

The accompanying drawing shows a die.-

gram of a preferred form of? the invention, wherein-- Figure 1 shows acomplete diagram of the invention, I 1

Figure 2 is a diagram of a suitable oppositely wound loop, and

Figure 3 shows the loop shield.

deterring to Figure 1, the upper part of the figure represents thetransmitting unit, lelt hand lower part of the figure is the power unit,and the right. handlower part the receiving unit. The transmitter apparatus is supplied with power ifrom a dyna motor and storage battery,which is charged from a suitable source of supply, andcontrolled by amain switch having one position for sending and receiving, and anotherfor charging. I I I The power supply switches 37 and ill) (Fig.2. 1) maybe manually operated, it desired, or automatically operated throughholding relays coactingg; with the switches biased by gravity or springmeans. to normally remain open. The holding relaysmay be controlled froma remote relay control switch 39 provided with a switch-hook, as suown.and so arranged. as to closcthe holdingrelay circuits when the receiver.78 is lifted from the hook, or to opensaidz circuits when the receiveris replaced thereon.- The antenna 1 is loosely coupled by output transformer 12 to the high frequency power circuit ol" tube 19. 1-1- thedynamotor with condensers 15, and its. output side supplies high voltagepower to the master-oscillator 1S, amplifier 19 and modulator 20.. 21..are condensers, 22 an ad ustable inductance :lor setting; the frequency,23 -1s a coupling con.-

denser of proper capacity to drive thepower amplifier tube 19. and 24 isa blocking con denser. The modulation" system is aconstant currcnt one,wherein the sum ofthe currents to the modulator and amplifier tubes 20,19, isconstant at voice frequencies. 25 is an adj ustabletuning-inductance to; tune the antenna to resonance as indicated byammeter 26. l

Transformer 12, instead of functioning: like the usual oscillationtransformer between :1 closed primary supply circuit and an antennacircuit, is similar to a power transformer Where the primary currentdrops very low on open circuit. This is effected by a high primaryimpedance at the band or range of operating frequencies when thesecondary is detuned or open-circuitcd. thus protecting tube 19 fromdestruction, it the antenna breaks or becomes dctuned. In addition, thesecondary fits loosely-overthe primary and the coupling is'finelyadjustable. This avoids the use of taps on :the secondary to adjust theantenna load for maximum plate circuit efficiency in tube--19,regardless of antenna characteristics within reasonable limits. Thisavoids variation of etficiency in using taps, and can be set atthe timeof installation to get the best output,

practice this is only necessary over quite long periods of time. Afurther advantage of the loose-coupled secondary is that in conjuno tionwith themaster oscillator-power amplitier, circuit radio frequencychokes in the cable between. the transmitting unit and power unit, arenot found to be necessary to confine the transmitter high frequency tothe antenna circuit. It is very desirable, of course, to eliminatethese-chokes especially those inseries with the filament lines becauseof the great power loss.

The positive terminal of the dynamotor 1% is connected to the plates ofthe tubes 19 and 20-through the voice'f'requency rcactance 28 by thewire l6-and to-the plate of tube 18 through the high frequency choke27by the branch wire 29. 30'is a *nmdulation transformer having highresistance 31 across its secondaryto improve the modulation. Theresistance 32 acts as a grid leak unit for independently regulating thegrid-filament operatingpotentials of all three transmitting tubes-18,19, 20 and obviating a separate battery to make the grids negative. Theprimary of transformer 30 is in series with battery 33 and telephone orother source'of speech 82. 34 is a resistance for regulating thefilament currents of tubes 18, 19, 20 as supplied by batteries 36connected to switchpoints 37. The leads 38 of battery 33 arelwistedasshown for apurpose hereafter to he described, and lead to switch points39. The points 4-0, 41 are for charging all the batteries in series,when connected with the respecti-ve points 3T. 39 from suitable powersource The switch points 39 close on points-l3 and points 37 on points4%, when the system is in operating condition.v

The batteries 35. 36 operate the dynamotor-lei andheat the filaments oftubes 18, 19. 20 and battery 33 operates the telephone transmitter 32and heats the filaments of the receiving 'tubes- All of the batteriesdischarge at the same rate because shunt resistance 15 is adjusted toincrease the discharge rate of the battery 33 up to-thatof batteries2:36. 46 is a voltmeter to indi-.

cate the conditionof charge of the batteries, atconstant load, and is acertain indicator, inasmuch as the batteries always discharge atthesaine rate- A mark on the dial indicates the operating pointbelowwhich the batteries should be chargedl For eliminatingcommutator ripple,the armature of dyni-unotor-l l isskew slotted, as about.tlu-ee-quarters of the slot pitch. which"inco'njunction withcondensers15 and choke: 28;completely smooths out the ripple in-thedynamotor-output current so that it is not heard inthe local receivingset,

The 7 receiving filament wires 38 are twisted as shown, toprevent loWfrequency induction in the receiving set from the Wires connected tobatteries 35, 36, which-run the d ynamotor.

The receiving unit is equipped with'a comparatively small loop aerialwhich? maybe of the ordinary type but is preferably of one of the formsshown in Figs-1 and 2 The loop Fig. 1, is double with each half wound inthe opposite direction and may be connected as indicated in circuit witha vari able tuning condenser 76 and loosely coupled through the coil 77to the input circuit of the detector 51. If the loop 5 (Fig. 2) which isalso double oppositely wound, is used instead of the loop 5 the freeends 49 and 150 of this loop are connected together and grounded, andthe mid-point of the coil joined tothe lead 51 which establishes aconnection to the grid of the detector tube 51 ot the receiver unit. Thereceiverloop (5 or 5) is shielded from local transmitter oscillations byany suitablemeans, but preferably by the electrostatic, open circuitedshield or cage 52,'Fig. This shield consists of a special form of cageor coil of conductive material ada'pted'to entirely sur round the loopand be slightly spaced from it. The preferred construction comprisesgroups of spaced, parallel conductors connected in series with one endonly of each group connected to the common grounded conductor-52. Thisarrangement provides an open circuited metallic cage surrounding theloop on all sides and serves to shield it from local transmitter energywithout irnpairing its effectiveness for the reception of incomingsignals. As indicated by the dotted lines in Fig. 1, the shield 52 mayenclose the loop 5 and its tuning condenser 76. the remainder of thereceiving equipment being enclosed in the metal box 47 provided withsuitable openings to bring in the connections from the transmitter andpower units and those from the desk telephone set.

The local oscillator 55 comprises a tube with inductance 56, variablecapacityj57 to change its frequency, and receives plate-circuit powerthrough the radio frequency choke coil 58 from battery The filamentcurrent. comes from battery 33 through switch points 39, 43, wires 38 ingrounded metal covered conductors 60, and adjustable resistant-e61. Theloop circuit is tuned by variable capacity 76 to the frequency of theincoming signal and is coupled to detector circuit through coil 7 7 Coil77fa1so receives local oscillations from nearby circuit of tube to forman intermediate heterodyne beat frequency in the output circuit ofdetector This beat. frequency is amplified by tubes 63, 64, coupled bytransformers 66. This intermediate frequency is then rectified by tube67 coupled to the output circuit of tube 65 by transformer 68. 69 is anintermediate frequency by-pass condenser across the primary oftransformer which couples tube 67 to audio frequency amplifier tube 71,the transformer 70 and tube 71 constituting an audio frequency stage ofampliiication. Transformer '72 adapts the output of tube 71 to telephonereceiver 73. The filaments of tubes 55, 51, 63, 6 65, 67, 71 are heatedby battery 33, while both parts of the battery 59, in series, supplyplate current to tubes 55, 63, 64, 65, 71, and one part supplies platecurrent to tubes 51, 6?. All of the receiving tubes employ filamentgridbias resistances 7-las shown to regulate the grid potentials.

The use of the local. oscillator 55 to heterodyne with the incomingsignal frequency is of advantage in that it avoids the necessity ofemploying a predetermined difference between the incoming and outgoinfrequencies, but the transmitter frequency can be employed with a properfrequency difference by cutting out oscillator 55 as by switch 7 5,.

and making the proper transmitter frequency adjustments. The maindifficulty, however, in using the transmitter to heterodyne the incomingcarrier wave, is in arranging the sending and receiving high frequencyequipment to give the proper amplitude of local oscillations in tube 51to produce maximum amplification, whereas by employing the localoscillator 55 the degree of coupling between the local oscillatorcircuit and 51 is such as to give maximum heterodyne amplification, andis fixed, no matter what are the conditions of installation of theequipment. Another advantage in employing the separate receivingoscillator is that the receiving set will function whether or not thetransmitter is going. This permits the sta tion to be in condition forreceiving a call When the transmitter is off. And still anotheradvantage is that by excluding the transmitter radio frequency out ofthe receiver the latter can be connected by well known methods to anordinary wire telephone system, without howling. The am plification ofthe beat frequency and then re-detection, is of advantage because ofgreater efficiency and quietness than either high frequency or audiofrequency amp lification will afford. This applies particularly to shortwave reception. For the longer waves, however, straight radio-frequencyamplification is quite satisfactory for this system.

As shown in Figure 1, conductors connecting the receiving unit with thepower and transmitting units are enclosed in metal sheathing to preventthe passage of high frequency currents. If the wires to telephone set32, 7 3 are short no metal covering is necessary on them. In practicethis provides a very compact and convenient receiving element capable ofbeing installed on a roof, with suitable weather proofing, or in a roomof a building with the transmitter set and the antenna on the roof atone side, without one interfering with the other. This is by reason oflocalizing the transmitter high frequency apparatus adjacent theantenna, which may either be run in connection with a ground as shown,or have a counterpoise, and controlling the transmission from whereverit is convenient to locate the operating position. If the transmittingand power units are separated somedistance, and the connectingconductors pass near the receiving unit, it will also be found necessary to enclose these conductors in metal sheathing preferably grounded.The object of grounding, of course, is to prevent trans mitter radiofrequency energy from passing through the sheathed conductors. Theshielded receiving loop is at one side pointing at the distant stationwith one side ap proximately toward the the antenna to pick up little orno energy from the transmitter. In this connection, it is important tonote that the master oscillator transmitting circuit with looselycoupled output transformer, or other means for confining the highfrequency transmitter power to its own radiating circuit, in conjunctionwith the metal sheathed cables between the various units, effectivelyprevents paralysis of the receivingloop systemby the transmitter, evenwhen located in and on the same building. Small loops in general andespecially of the form disclosed herein are very desirable forreceiving, in that they pick up much less induction, etc., in operatingpositions such as factories, than do antenna-ground systems. Looselycoupling the receiving set to the loop increases the selectivity, and isfound desirable in locations where there is considerable interferencefrom other stations and induction. In using loose coupling, as betweenthe tuned loop and a secondary coil, care should be taken to avoid anystray capacity coupling. A preferred arrangement is to mount the littlesecondary coil 77 outside of the loop shield, together with the rest ofthe receiving equipment in a metal box, but this loose coupling can beanywhere in the high frequency circuits between the loop and thetelephone receiver;

Should there be found to be interference with the receiver from a verypowerful local transmitter the receiving and sending elements can befurther separated, but can still be much closer together and give duplexcommunication, as with wire telephones, than has heretofore beenpossible with other systems proposed, which have required considerableseparation of transmitter and receiver, and expansive land andconstruction.

After this system is once adjusted upon installation, no furtheroperating adjustlong periods of time.

nients 1:51.136 'toun'd -necessary, excepting: over A power unitconsolidated 1 for both sending-and-receivrng'is bGlH-BVCdtO. be newoperating, as herein shown anddescribed. If

desirable a specially designed inotor-generator could be built to run onthe-available source of gower a n'd-si-ipply suitablezpowcr to -ru-ntheequipment; but storage batteries Il-ILUO the 'ad vantage cl---rez-idern.i 1 the communication vindependent of power supplyinterruptions.

WV-hat I claim is:

1. 1n duplex a-a'dio ;telephony, relatively power'tul means forradiating outgoing oscillationsand means for receivingincomingoscilations loatcd insu'chproximity that the-receiving means tends to beparalyzed by the outgoing oscillations, at telephone receiver connectedto be responsive to the incoming oscillations and an adjacent telephonetransn-ntterconnected tocontrol the outgoing oscillations, means t-orsupplying power-to operate the sending and receiving systems,-sai ilreceiving means inclu-ding an antenna provided vwith an open clrcuitedmetallic shield.

In duplex radiotelephony, the combination eta sending element and aradio transmitter connected thereto, anrantenna providedwit-h an opencircu-ited metallicshield, a radio receiver connected thereto. means forsupplying power to thesystem, and a telephone transmitter and receiver.

3. In duplexradiotelephony, the combination of a transmitting elevatedelement, a ltKllO transmitter connected thereto, means tor-settingthe-frequency of outgoing oscillations 7 independently of 1 theradiating circmt. characteristics, a loop-receiving circuit,

a shield including an open circuitedconductive member associated withsaid loop, a

power supply, and a telephone transmitter and receiver.

In duplex radiotelephony. the comhinatfon ot aradiating!-element,:aradiotransmitter circuit connected thereto,said'transmitten circuit including -a:masteroscillator, an amplifier andiarmodulatorameans:tor iinductively coupling the transmitter to saidelement.;a:rad-io receiving circuit having a loop antenna, an opencircuited conductive shielding member enclosing said loop ani the @001)illlBlGOfvGIltklOSGCli by; pluralityuof preventing l local paralysis.of, the receiving independent conductive shielding members and theremainder of said circuit enclosed in asi-ngle conductive shielding;member? for circuit by the transmitter, a source 01 power,

and a telephone transmitter and receiver.

"6. In duplex radiotelephony, the combinationof a ra'diating element,: aradio 1 trainsni'itter connected: thereto, a; loosely. coupled output 1transformer iliaving adjustable; secondary an d high impedance:primarywhen the secondary circuit is detuned, saidtransanit-tercomprisingan cscillatonyan amplifier -a'nt l zv n iodulator tube, a grid:leak regrriating resistance -u nit,-.a loop receiving circuit having'mcans incl udingza grounded, open-.cin cuited, conductive shieldv for:PIQVGlltIllglO- 'cal paralysis of the. receiving circuitahy thetransmitter, a-source otpower, and a telephone transmrittena-ndreceiver.

' 7. 111 duplex radiotelephony, the combination of a: radiatingelementzloosely coupled to a transmitter, said transmitter including amaster oscillator a consolidated power 'unit' tor thesystem, a receivingunitiliavi'ng a loop antenna. shielding means tor prevent in;electrostatic coupling lJGtWGGIhSZl-ldrtiflltenna and adjacent metallicobjects, means for loosely coupling the antenna; tozthe re- 'ceivingcircuit. from .the outside of said shielding means," the conductorspassing between tliepower and receiving 'unitsubeinzg shielded,and-atelephone transmitter and receiver.

*8. In duplex: ra'diotelephony, the combiiua :tion of a radio.transn'iitter .andaa radiating element, double oppositely wound.receivlng loop havinga receiving set coupled thereto,aconsolidatedipomver unit contain ing dynamotor and -:storage batteriesfor energizing both the receiver and transmitter,

-'sheathed conductors passing between .the transmitting, power andreceiving un-1ts,- the conductor-sin the power unit which :go to the IT0081 ving :unitbeing twisted in a manner to namotor no ses. in thereceiving prevent d set, and iii telephone transmitter .and receiver.

- 9. \In duplex radiotelephony, the combination of a transmitterwand aradiating. eletenua. a source of power opcratively connectment, ashielded loop positioned so as to prevent local paralysis of thereceiving set connected thereto, a consolidated power unitCO'l'l'lPllSlIlg storage batteries and a dynan'iotorfthe dynai'notorarmaturebeing skew slotted, condensers shunted across both the input andoutput side of'the dynamotor, the high voltage circuit containing a lowfrequency choke coil. and a telephone trans mitter and receiver.

10. A duplex radio telephone station comprising separate transmittingand receiving elements. means tor preventing local paralysisof thereceiving set by the transmitter,

the receiving set consisting of a double, op-

loosely coupled thereto through an output transformer, a separatereceiving set co1nprising a local oscillator, a receiving loop shieldedfrom the transmitter oscillations, amplifying and telepl'ione detec ingmeans, a telephone transmitter controlling the outgoing oscillationsthrough a power modulator, a power unit supplying the transmit-- tingand receiving circuits, and means for preventing the transmitting powerfrom a ffecting the detection of the received signal oscillations.

13. In duplex radio telephony, the combination of a 'adio transmitterunit having a radiz iting antenna, a radio rcceiring unithaving a. loopantenna, a conmion piivver supply for both said units, switch means forcontrolling the supply of power to each unit, rely means including aswitch hook for remotely controlling the switch means, a telephonetransmitter and receiver opcratively connected "to the transmitting andreceiving circuits, said receiver enacting with said switch hook in suchmanner as to cause said relay means to open or close said switch means.

1.4:. The combination With a relatively powerful source of oscillationsand a radiating element therefor for transmitting, of a loop receivingelement adjacent said element and \vithin the field thereof positionedrelatively to said element as to receive a minimum of local transmitterenergy, amplifying and detecting means connected to said loop, and meansfor-shielding the receiving "system from local transmitter highfrequency oscillations from said radiating element including an opencircuited wire cage surrounding said loop receiving element.

l5. In radio telephony, the combination of it separately excited poweramplifying circuit delivering continuous carrier wave scillations to aradiating element through an output power transformer, a loop receivingelement positioned to pick up a mini mum of local trai'ismitter energyand tuned to receive a different incoming frequency, a power supply, andgrounded, open circuited shielding means for preventing local paralysisof said element.

16. A duplex radio telephone station consisting of tral'ismitting, powerand receiving units, the transmitting unit having means for generatingoutgoing modulated oscillations controlled by a telephone transmitterand. an oscillator for setting the frequency independently of antennacircuit character istics, the receiving unit consistii'ig of aSllleltltll loop, detector and amplifier and telephone receiver, theunits being co.u ncctcd by power supply and control wires and means forpreventing high frequei'icy oscillations from passing through saidwires, :1 switch hook for said receiver, and switching means operated bysaid hook for energizing or decnergizing the traiisniitting andreceiving eircui s simultaneously when the receiver is removed from orreplaced on said hook.

1T. lira duplex radiotelephone system including a. transmitting set,loop receiving and a cmnmon source of power suppli for both said sets,the l'llGlillOClOf operating said system Without paralyzing thereceiving by local "transmitted energy which consists in balancing outsaid traiismittei'l energy in the power supply circuit and in the loopcircuit, shielding the receiving circuit in a closed circuited metallicconductor and shielding the loop circuit in an open circuited metallicconductor.

Signed. at New York in the county ol New York andstate of New York this26th day of August A. D. 1921 PAUL XVARE.

Ill)

CERTIFIGATE Gi CGRRECTIQN.

Patent No. 1,627,718. Granted May 10, 1927, to

PAUL WARE.

It is hereby certified that error apgiears in the printed specificationof the above numbered patent requiring correction as follows: ?age 3,line 17, before the words "The positive" insert the Words "27 are radiofrequency ehoke coiis"; page 4, line 88, strike out the article "thesecond occurrence; page 6, line 15, claim 12, for the word "amplified"reaii "amplifier"; and that the said Letters Patent should be read withthese eorreetieie therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 31st day of May, A. D. 1927.

M. J. Moore, Seal. Acting Gommiseioner of Patents.

I GERTIFIGATE 8F GURREGTION.

Patent No. 1,627,718. Granted May 10, 1927, to

PAUL WARE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: iage 3,line 17, before the words "The positive" insert the words "27 are radiofrequency choke coils"; page 4, line 88, strike out the article "the"second occurrence; page 6, line 1b, claim 12, for the word "ampiifiedreed "ampiiiier"; and that the said Letters Patent should be read withthese corrections therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 31st day of May, A. D. 1927.

v M. J. Moore, Seal. Acting Commissioner of Patents.

